Surfactants are widely used in aqueous based personal care, household care and industrial and institutional care formulations as wetting agents, detergents, and emulsifiers. In personal care cleansing products (e.g., shampoos, body washes, facial cleansers, liquid hand soaps, etc.), household care cleaning products (e.g., hard surface cleaners, laundry detergents, dish soaps, automatic dish washer detergents, shower cleansers, bathroom cleansers, car wash detergents, etc.) and industrial and institutional care cleaners (high strength cleaners, detergents, etc.) the surfactant chassis is the most important component in these detersive formulations.
Although in principle any surfactant class (e.g., cationic, anionic, nonionic, amphoteric) is suitable in cleansing or cleaning applications, in practice most personal care cleansers and household cleaning products are formulated with anionic surfactants or with a combination of an anionic surfactant as the primary detersive agent with one or more secondary surfactants selected from the other surfactant classes. Anionic surfactants are often used as detersive agents in cleansers and cleaning products because of their excellent cleaning and foaming properties. From the consumer's perspective, the amount and stability of the foam directly relates to the perceived cleaning efficiency of the composition. Generally speaking, the larger the volume of foam produced and the more stable the foam, the more efficient is the perceived cleaning action of the composition. This presents a potential problem in low-surfactant formulations, as foam volume tends to decrease with decreasing surfactant concentration. Exemplary anionic surfactants traditionally utilized in these formulations include alkyl sulfates, alpha-olefin sulfonates, and alkyl benzene sulfonates. In order to provide high quality lather or foam, conventional skin cleansing products typically contain from greater than 10 wt. % to about 25 wt. % (based on the weight of the total composition) of a surfactant chassis, including relatively high levels of anionic surfactants. While the anionic surfactants and in particular the anionic sulfates and sulfonates are efficient detersive agents and produce large foam volume with good foam stability properties, they tend to be harsh to the skin and eyes. Cleansing compositions containing higher levels of surfactant tend to be harsher in terms of irritation to the eyes and skin. The high levels of surfactants used in these products tend to dehydrate and remove lipids from the skin. The surfactants act to emulsify the natural oils in the skin, which are washed away when the cleansing composition is rinsed off.
It is known that the irritation caused by anionic sulfates can be reduced by ethoxylation. However, the use of ethoxylated anionic surfactants is accompanied by a corresponding reduction in foam volume. For example, sodium lauryl sulfate, a high foaming surfactant, provides good lather but may be harsh. In contrast, sodium lauryl ether sulfate (the corresponding ethoxylate) mitigates harshness, but at typical ethoxylation levels, e.g., ethoxylated with 3 to 12 ethylene oxide units, is a poor foaming agent (see Schoenberg, “Baby Shampoo,” Household & Personal Products Industry 60 (September 1979); U.S. Pat. No. 4,132,678; and U.S. Pat. Appln. Pub. 2009/0155383). Additional attempts to attenuate the harsh effects of anionic surfactants have been made by replacing some of the foam generating anionic surfactant with very mild secondary surfactants. The anionic surfactant is utilized in conjunction with a nonionic and/or an amphoteric surfactant as disclosed in U.S. Pat. No. 4,726,915. Other efforts have focused on reducing the amount of the overall surfactant level in response to the perceived negative impact of surfactants on the environment. However, reducing the relative amount of anionic surfactant in a cleansing or cleaning composition adversely affects the foaming properties of the composition.
Another attribute that consumers expect of their cleansing products is an aesthetically pleasing viscosity. Formulations that flow with a watery consistency are aesthetically unpopular to consumers with expectations of rich and creamy products. While low viscosity products may be effective for their intended purpose, they are perceived to be of low quality by the consumer. Formulations that flow with a watery consistency run off when applied to the hair and skin. For a cosmetic cleansing composition to be effective, it often must have substantivity. Rheology modifying thickeners provide this substantivity.
Rheology modifiers are used in aqueous cleansing products, such as, for example, shampoos, body washes, facial cleansers, and liquid hand soaps, to increase the viscosity to make them easier for the user to handle and/or to increase the yield stress of the composition. While a certain rheology modifier may thicken or enhance the viscosity of a composition in which it is included, it does not necessarily have desirable yield stress properties. A desirable yield stress property is critical to achieving certain physical and aesthetic characteristics in a liquid medium, such as the indefinite suspension of particles, insoluble liquid droplets, or the stabilization of gas bubbles within a liquid medium. Particles dispersed in a liquid medium will remain suspended if the yield stress (yield value) of the medium is sufficient to overcome the effect of gravity or buoyancy on those particles. Insoluble liquid droplets can be prevented from rising and coalescing and gas bubbles can be suspended and uniformly distributed in a liquid medium using yield value as a formulating tool. A yield stress fluid is used generally to adjust or modify the rheological properties of aqueous compositions. Such properties include, without limitation, viscosity improvement, flow rate improvement, stability to viscosity change over time, and the ability to suspend particles for indefinite periods of time.
Rheology modifiers prepared from homopolymers and copolymers of acrylic acid have been utilized to provide rheological properties including thickening and the suspension of particles and droplets in surfactant containing compositions. Homopolymers of acrylic acid crosslinked with an allyl ether of pentaerythritol, an allyl ether of sucrose, or an allyl ether of propylene (INCI Name: Carbomer) have been utilized as rheology modifying and suspending agents in shampoo compositions comprising an anionic detersive surfactants as disclosed in U.S. Pat. Nos. 8,153,572; 8,298,519; and 8,349,301. While these polymers provide good rheological properties, there is a need to enhance foaming properties in the cleansing compositions in which they are included.
Recently hydrophobically modified, crosslinked copolymers of acrylic acid have been proposed for use with anionic surfactant containing cleansing compositions to mitigate the adverse effects of harsh surfactants while maintaining high cleansing and foaming properties. In International Pat. Appln. Pub. No. WO 2005/023870 it is disclosed that certain hydrophobically modified materials capable of binding surfactant can be combined with anionic surfactants to produce personal care compositions that exhibit relatively low ocular and/or dermal irritation while maintaining relatively high foaming and foam stability properties. Disclosed hydrophobically modified materials include hydrophobically modified crosslinked acrylic copolymers that are synthesized from at least one ethylenically unsaturated carboxylic acid monomer and at least one ethylenically unsaturated hydrophobically modified monomer. The disclosure states that exemplary hydrophobically modified acrylic polymers are set forth in U.S. Pat. No. 6,433,061 to Noveon, Inc. The WO 2005/023870 disclosure additionally exemplifies polymers available under the trade names Carbopol® Aqua SF-1 and Carbopol® ETD 2020 both provided by Noveon Consumer Specialties of Lubrizol Advanced Materials, Inc. as suitable polymers for use as a surfactant binder.
The polymers disclosed in U.S. Pat. No. 6,433,061 as well as the polymers identified under the Carbopol® Aqua SF-1 and ETD 2020 trade names are crosslinked. At column 5, line 32 of the '061 patent it is disclosed that the “The copolymer of the present invention desirably is crosslinked by a crosslinking monomer.” Moreover, all of the polymers exemplified in the '061 patent disclosure contain a crosslinking monomer. In the trade literature Carbopol® Aqua SF-1 polymer is described in Noveon Consumer Specialties of Lubrizol Advanced Materials, Inc. Technical Data Sheet TDS-294 (July, 2003) as: “ . . . a lightly crosslinked acrylic polymer dispersion designed to impart suspending, stabilizing, and thickening properties to a variety of surfactant-based personal cleansing products;” and Carbopol® ETD 2020 polymer is described in Noveon Consumer Specialties of Lubrizol Advanced Materials, Inc. Technical Data Sheet TDS-187 (January, 2002) as: “ . . . an ‘easy to disperse’ crosslinked polyacrylic acid copolymer processed in a toxicologically-preferred co-solvent system.” The foregoing acrylic based crosslinked polymers are non-linear, branched polymer chains which interconnect to form three dimensional network structures and have long been used in personal care applications for their rheological and structure building properties. Upon neutralization, these anionic water soluble or dispersible polymers possess the unique ability to greatly increase the viscosity of the liquid in which they are dissolved or dispersed, even when present at concentrations considered to be quite low.
U.S. Pat. No. 8,293,845 and U.S. Pat. Appln. Pub. No. 2012/0157366 describe the use of low molecular weight linear (non-crosslinked) acrylic acid polymers and copolymers in cleansing compositions formulated with anionic surfactant containing cleansing compositions to mitigate the adverse effects of harsh surfactants while retaining foaming properties without substantially affecting the rheological properties the composition. These anionic linear polymers also require neutralization with a pH adjusting agent within a relatively narrow pH range to provide optimal irritation mitigation properties. These linear polymers convey no yield stress properties to the cleansing composition in which they are contained.
There is a need for a polymer that improves foam properties and/or yield stress properties of surfactant containing compositions formulated with an anionic primary surfactant, and which imparts mildness and is not pH dependent.